Engine will only idle

[SAFARI]

This is my first post and I have run out of plans to correct my problem. I have an older A-4, the boat is a home built '66 Spencer with some upgrades. It ran perfectly last fall and then when it was launched this spring it would not start. Rebuilt mech. fuel pump and it would start and only idle. So rebuilt the carb and still the same. There didn't seem to be any problems when cleaning the carb etc. Changed the mech pump with electric and still it will not provide any acceleration beyond an idle with max rpm at about 800. Fuel filter has been changed as all the fuel, installed new plugs and rechecked the timing. Anyone have any ideas. I have been in contact with the previous owner who owned it for 45 years and he is also at a loss as to what would be the problem. I have checked and rechecked the adjustable main jet but no change. Does anyone have an idea of what I am missing?

[Dave Neptune]

Have you checked the hose clamps on all fittings? Any sort of air leak will drastically affect the fuel delivery (volume) and/or pressure which feeds the carb.
Do you have more than one filter?
I suggest checking the fuel pressure as an installed cheap gage will really help on this and future fuel related issues.
Another possibility is the fuel pick up in the tank having a pin hole causing a loss of pressure. Or the screen on the end of the pick-up tube if so equipped.
did you try engaging the choke when throttling up if you get a bit more power even for a short time you probably have a fuel delivery issue.

Dave Neptune

[tenders]

You might be running on fewer than four cylinders. Triple check that the plug wires are correctly in 1-2-4-3 order and in the right places on the distributor. Pull each plug wire off one at a time to make sure each is contributing to the process. Wear rubber gloves.

**note, that is not 1-2-3-4 order**

Also check for an exhaust blockage. Perhaps a clog formed over the winter and the engine is gagging on its own backpressure.

[thatch]

One thing that has not yet been mentioned is the flame arrestor. Removing it for testing or cleaning it with carb cleaner will eliminate it as a possibility.
Tom

[SAFARI]

I have tried to eliminate the fuel tank as a potential problem by feeding fuel from a small jerry can directly to the pump but it produced the same results. Will check on the other items mentioned this weekend to see if it changes the current status. I certainly appreciate the input as my experience is some what limited.

[capnward]

Dave is right about checking if applying the choke makes a difference. Air leaks are also a possible culprit. You say you checked the adjustable main jet. Did you turn it all the way into the seat to dislodge any obstruction there, then turn it out 1 and 1/2 full rotations, maybe 2? Turning it out makes the mixture richer, which should make a difference. If it doesn't, you are running too lean which could indicate a fuel restriction or an air leak.

[zellerj]

How about a blocked exhaust. An engine is an air pump. If air can't get out, none is going in. Would be messy to test, but removing the exhaust hose and see if the rpms increase. I would have the admiral do this while you are drinking a beer in the cockpit.

[Sam]

I have tried to eliminate the fuel tank as a potential problem by feeding fuel from a small jerry can directly to the pump but it produced the same results. Will check on the other items mentioned this weekend to see if it changes the current status. I certainly appreciate the input as my experience is some what limited.

Just a thought - re hook up your jerry can and place it or smaller can up on hatch cover and feed fuel line directly down to carburetor - syphon or bulb or hand pump fuel to the carb and rely on gravity pressure [ie. std gravity feed arrangement]. The engine should start and if it revs up the pump is the issue

[capnward]

I doubt the pump is the issue, as the problem is the same after SAFARI changed to an electric pump after a mechanical one. A fuel pressure gauge would help diagnose a fuel restriction. A more likely cause is a blockage in the main jet or a filter, or an air leak. He says the fuel filter has been changed, as if there is only one filter in the line. I have three, the Racor water separator, and two inline filters, on before and one after the mechanical fuel pump. I change all three when I "rebuild' the carb. An exhaust blockage is possible but less likely. If the engine will idle, the solution is not far away.

[SAFARI]

I followed the advice of removing the flame arrestor and cleaning it. There was a fair amount of carbon buildup and once I reinstalled it back on the carb, the engine came to life. I sincerely hope that this was the outstanding problem. Again I want to thank all those who came forward with suggestions. Not sure what procedure I will follow in covering it come lay up in the fall.

[capnward]

It's alive!

I also hope cleaning the flame arrestor was the solution. It makes sense, because now the engine can breathe better. The residual carb cleaner in the arrestor might have acted as starting fluid. If so that effect will diminish quickly.